Alex Luthor Jr. didn't so much go crazy over time as he realized his interests were not those of everyone else. His father HAD a world, Alex never did. Alex wasn't crazy, it's just that he couldn't get what he wanted without harming others. That might make him evil, but I don't recall him ever being irrational--quite the contrary, it was a meticulous plan.
And he really did believe what he was doing was best for everyone. It's really an issue of perspective with him. Besides, before you call him evil, then what's a DC editor who does the same thing? Or a fanboy who insists on the reversions that Alex and Prime(who IS how the DC editors view the fanboys who want characters to be changed back to their favorite versions, and I'm surprised this hasn't been commented on more) wanted?